Adding a conical bevel/fillet to a mesh?
Blender doesn't currently (Nov 2015) have a fillet that does variable radii, but you could approach the same effect with the Subdivision surface modifier to some degree. If you guide the geometry the result will look quite good.

My approach would be to Shrink-wrap a Polysphere over the exported Object.



Below:


On the left is the original import, 
in the middle is a polysphere (a Cube subdivided a few times and then vertices are transformed with a 'To Sphere' operation), 
to the right is the result of a Shrink wrap from the Polysphere onto the Original geometry




With a bit of experimentation with the ShrinkWrap modifier and tweaking of the Polysphere, you could get very close to what is desired. Because Blender isn't a solid modelling CAD program it is bound by the underlying topology with respect to what can be filleted nicely.

Even on this mesh adding a Subdivision Surface modifier produces visually OK results, this probably doesn't meet tolerance requirements.



Tweak the polysphere (translating up/down mostly) and the offset value, till it approaches acceptable results.

The ShrinkWrap object's shape is important  

You'll find that being more specific about the geometry of the Shrinkwrap object will help the eventual wrapped geometry. Here i started by making a copy of the 8 extreme vertices of the imported object, and make a Cube using those vertices. Subdivide the sides and scale extruded the top inwards.